1. Field of the Invention
The present invention relates to a camera adapted to expose film of widely different film speeds in which apparatus is provided for selectively positioning an exposure-regulating filter over a lens (aperture) of the camera when a flash unit is mounted on the camera and for preventing positioning of the filter when film of relatively low speed is in the camera.
2. Discussion of the Prior Art
By being selective in the combination of diaphragm settings and shutter speeds provided, a camera can be designed that will automatically adjust exposure parameters to properly expose film of more than one effective ASA rating. However, the design may be impractical from an economic or performance standpoint for a number of reasons. From a performance standpoint, for example, a very small aperture and fast shutter speed may be required to produce the proper total exposure of high-speed film in normal lighting. If a cadmium sulfide photosensor, which has a slow response to low ambient or changing light is used, shutter speeds attainable are not fast enough to provide proper exposure with the smallest useful diaphragm settings available. The required diaphragm opening would be so small that diffraction would result. Alternatively, if a silicon photosensor, which has a fast response to light is used to achieve faster shutter speeds, the speed desired may be difficult to achieve mechanically.
Therefore, it becomes advantageous to utilize neutral density correction in the exposure system to provide the number of available stops of exposure to accommodate the different film speeds. Neutral density correction may be used for a lens aperture or for a photosensor that is part of an exposure control circuit. Thus, it is desirable to have exposure-control apparatus that senses the speed of the film being used and also senses when a flash unit is mounted on the camera and selectively positions respective filters over the lens aperture or photosensor as required to effect proper exposure for the speed of film in the camera.